CB175 performance build questions
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CB175 performance build questions

This is a discussion on CB175 performance build questions within the Technical forums, part of the Caferacer.net Forums category; Ok so im going to be starting on my CB175 motor this week and wanted to talk about some upgrades to do while its being ...

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Thread: CB175 performance build questions

  1. #1
    Senior Member jaguar's Avatar
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    CB175 performance build questions

    Ok so im going to be starting on my CB175 motor this week and wanted to talk about some upgrades to do while its being rebuilt.

    Not looking for a full race motor but something fun for the street.

    Motor has low compression and needs the kick shaft replaced so its going to be all the way open.

    Was thinking about trying to find a slightly higher compression piston? but haven't seen much. Or am i better off with 1mm OS OEM pistons?

    Figured some port matching and smoothing could help, don't thing valves are in order. but open to comments

    I wanted to talk about carbs too, at what point would SL350 carbs not be overkill?

    Seen some internal lightening tricks from group W and wanted to know if they will be ok on a street motor.

    mega cycle seems to only list cams for the "sloper" motor, do they make one for the "vert" or will cb200 parts work?

    My motor is a 72 cb175
    I love the idea of what I call OEM+, using OEM parts off other bikes to mix and match and create something better. That why i mentioned the use of SL350 carbs

    What would you guys build for a hot street set up?
    Thanks very much for any help or ideas
    I am Derby\'s Bitch


    Some times things come around that are so singularly inept it gives you a whole new appreciation for the ept

  2. #2
    Senior Member nic579's Avatar
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    Do a search on the site there is a bit of this talked about already, but you may have to pick through a few long threads to get to it. Also look at JBs site on building his race bikes.

    http://www.jrbranson.com/HondaRacer/mainpage.htm

  3. #3
    Senior Member nic579's Avatar
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    Here is another good place too:

    http://autos.groups.yahoo.com/group/F-160/

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  5. #4
    Senior Member YucA's Avatar
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    I wanted to go crazy when I cracked mine open as well. Pretty much same story- low compression and kick starter shaft was stripped. For the power these things make, I decided it just wasnt worth the extra money to go all out. My sleeves we still within spec so I just scored the stock rings and a flexhone to knock down the glaze a bit.

    Youre gonna get a hot cam, Electronic ign, coil, pistons, rings, new carbs and all the misc shit that will be needed for what, >5 more hp to the wheel? Can't see that being worthwhile for a street bike that will get ragged on. I know I beat mine to hell when I ride it. Kind of have to, but that's half the fun of these little pos's- being able to beat the hell out of em on the street and not worry about you precious fully built "race" motor.

    I'd say build it relatively stock, clean up the ports, get some 22-24mm carbs and get em running right. That SHOULD yield a slightly better top end.

    If you have the money burning a hole in your pocket, then disregard this post.

  6. #5
    Senior Member Teazer's Avatar
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    Let's keep things in perspective here. The average "race" 175 is a much lower state of tune than teh avreage street bike built today. Mainly because there isn't a lot that you can do.

    Compression. Go with OEM pistons and dry build to the top of the barrels (no rings but use a base gasket). Measure the deck height and if the piston is below the deck, have the barrels machined to correct that. I like to go lower than that and them machine the squish band on the piston at a different angle. Then I have some machined off the head - 1mm is fine. and get the squish bands machined concentric with the bores.

    Clean up obvious flash etc in both ports and spend some time making the exhaust flow better.

    24mm SL carbs are a great upgrade, so match the manifolds and ports reasonably well. We built a race 204cc CB160 5 speed with stock carbs and it wasn't much slower than our regular race bike with 26mm crabs.

    Cams are easy - you order the mildest megacycle cam. We race with that came because it makes more midrange than any other and loses nothing up to 11k and beyond. You will want decent valve springs to go with that.

    Valves do lose their heads if you rev the nuts off it all the time. We lost one at RA and it destroyed head barrels other valves, con rod etc. But that was after dozens of dyno runs and hundreds of track miles. Get a GL1000 Dyna S and you will be surprised to find that the backing plate is a perfect fit. The rotor needs minor modification.

  7. #6
    Senior Member jaguar's Avatar
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    teaser thanks for the info.
    GL1000 eh? sounds good. i like finding out what hits and what fits....its fun for me.

    What needs to be done to fit the SL carbs? base line jets?

    Like i said im not looking to build a balls to the walls race bike, more looking for small improvements that will result in a smoother and better power band.

    What about some of the light weight stuff that group W talks about?
    like removing one of the gears on the clutch basket?

    And for the cams i don't see mega cycle showing anything for the "vert" 175. So should i use a "sloper" cam or a CB200?
    Is there a "hot" cam from a different year bike? kind of like how the cam in the type one cb350 is better?

    I am a member of the yahoo group. its been slow lately but i do need to talk to those guys
    I am Derby\'s Bitch


    Some times things come around that are so singularly inept it gives you a whole new appreciation for the ept

  8. #7
    Senior Member Teazer's Avatar
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    AFAIK, and I'd need to check the Megacylcle site, the base cam is the same profile for all motors. Of the top of my head, I think they are listed as 122-00 or 135-x1, but I'd have to check that again.

    IIRC the 175 CB cam was the "hottest" of those motors, but they are all really tame. Honda race kit cams for other bikes are also really mild. eg when we raced a CB77 we tried 5 or 6 different cams including a Race kit 20-40 (810) cam and it was nice and mild. Really good design, but not very exciting.

    Clutch gears are fine as they are. That's a lot of work for a few grams. I do it to ours, but I need all the help I can get. Thinking about it, it's only labor so if you have the time go right ahead and do it. BTW, we also drill the living crap out of the single gear that's left. Can't say I can feel the difference but it all adds up right?

    Dump the rear fender and ask Brett/Brent (I'm no good with names) at Glass From The Past. He just introduced a great rear fender of the 160 group and I suspect it would work on a V175.

    An aluminum or carbon front fender blade would be nice and holes in the hubs and brake plates and shoes help. We run Al rear sets and drilled axles and drilled or Al wheel bearing spacers etc. The reason behind those is that winters up here are long and drill bits are cheap. You can also drill or grind a fair amount out of the brake cams and drill them down the shaft.

    Al side cover screws look tacky but weight adds up. Ti is a great way to lose weight - especially from a wallet.

    Baseline jetting for SL carbs? You jest of course..... Tell me what's in them and I can take an educated guess - OK so that's an exaggeration, but I can try to sound intelligent as a I pull numbers out of the air. What I'll actually do is to look at what we use in the 26's and in 22's on other bikes and see if there's enough of a pattern to suggest something.

    I'll need a list of all the jets and dimensions including the needle taper or measure it the way Mikuni do and I can see what that looks like. We had to tweak the needle shape on the 26's and used taller needle jets to shape the fuel slope. I also spent a small (very small) fortune trying different air jets which were specially machined for us.

    Getting the main jet and main air jet right is not so hard on the dyno, but midrange takes a little more on-road time with a notepad and marks on the throttle housing. The notepad is the most important tool you have available. Use it wisely....

  9. #8
    Senior Member jaguar's Avatar
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    So you don't think the SL carbs are to large for a 1mm overbored motor?
    Don't really want to run into the issues that the 350 guys are when they fit 32mms

    Yeah those labor things are part of what im talking about. im going to be there and yeah it all ads up
    the removal of that clutch gear i read takes off like 2lb.
    figured a home done blueprint wound make things smoother and nicer
    I am Derby\'s Bitch


    Some times things come around that are so singularly inept it gives you a whole new appreciation for the ept

  10. #9
    Senior Member jaguar's Avatar
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    do you have any pics of the internal gear drilling that you are talking about?
    I am Derby\'s Bitch


    Some times things come around that are so singularly inept it gives you a whole new appreciation for the ept

  11. #10
    Senior Member Teazer's Avatar
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    quote:Originally posted by jaguar

    So you don't think the SL carbs are to large for a 1mm overbored motor?
    Don't really want to run into the issues that the 350 guys are when they fit 32mms
    If you have a set of SL carbs, let's talk about what's in them and what they are like and take it from there. Stock work fine too.

    If it were mine, I'd have a good look at both sets and I'd look at your ports and work out the port shapes that would work best and I think I'd end up with the SL24s. The modification back in the day was to fit CB72 22mm carbs because they were available, and that was on CB160s.

    In fact I think I still have a set of manifolds to fit 22 on a sloper 160 motor here somewhere but they are no use for a V175.

    What it comes down to is how will you use the bike - putting around town or screwing it's skinny little neck? If you want really good low rev riding, go stock. If you like to get the revs up, go SL. It's a case of horses for courses.

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